PECTIN. 881 



alcohol, by an alcoholic solution of ethalate of potash or soda. 

 The ethalates of the alkalies are decomposed by a large quan- 

 tity of water, although they dissolve in a small quantity without 

 change. (Dumas and Stas, An. de Chim. &c. Ixxiii, 124). 



Cetene, C 32 H 32 . This hydrocarbon was obtained by MM. 

 Dumas and Peligot, by distilling ethal repeatedly with glacial 

 phosphoric acid, which deprives the former of 2 atoms of water. 

 It is an oily, colourless liquid, boiling at 527 ; the density of 

 its vapour is, by experiment, 8007 ; by calculation, supposing 

 its combining measure 4 volumes, 7843. It is insoluble in 

 water, soluble in alcohol and ether. 



CHAPTER VII. 



OTHER INDIFFERENT SUBSTANCES. 



CLASS i. ORDINARY CONSTITUENTS OF PLANTS. 

 SECTION I. 



PECTIN. 



Formula : HO-f-C 12 H 17 O n . This name was applied by Bra- 

 connot to a principle which forms the basis of vegetable jelly.* 

 It is extensively diffused in the juices of pulpy fruits and roots, 

 especially at the time of their maturity, and occasions these 

 juices to coagulate, when mixed with alcohol or boiled with 

 sugar. It may be prepared from apples, for instance, by heating 

 the juice with a little albumen till the latter coagulates, filtering, 

 and precipitating the pectin by a considerable addition of alcohol 

 to the liquid. By a second solution in water, and precipitation 

 by alcohol, the pectin is completely purified. When only a 

 small quantity of alcohol is added to the watery solution, the 

 juice fixes as a jelly after an interval of one or two days. 



After being washed on a filter and dried, pectin is semi- 

 transparent, arid has a considerable resemblance to isinglass. It 



From TrriKTiQy coagulum, 



2 >l M 



